Heterocyclic compounds are often the key structures responsible for many natural products and pharmaceutical reagents biological activity. To synthesize derivatives, chemists well either start from the cyclic starting materials or from open chain linear structures followed by cyclization methods.
A number of catalyst systems are known for the preparations of cyclic compounds from combinations of unsaturated hydrocarbons, including olefins, alkynes and derivatives thereof. Representative cyclization methods using dienes including catalytic olefin ring closing metathesis and phosphorus/cyclopentyl group based/ligand free metal or lanthanide hydride or their derivatives catalyzed cyclization. These methods have been found to be extremely important in natural products/drug molecules syntheses, and fine chemical preparations. They both strongly favor the production of the smallest possible D-member rings (D=integer, via small molecules elimination or tail-to-tail cycloisomerization), but larger (D+1)-member rings are generally cannot be synthesized by these methods, except all-carbon linear cyclization precursors or specialized precursors with preformed cyclic back bones or under extreme Lewis acidity. Especially in case of an oxygen atom containing cyclization precursor is employed, those extreme Lewis acidity will lead to substrate decomposition or catalyst deactivation by means of unproductive chelations, and produce no desire (D+1)-member rings.